   (for [objs (context-extents ctx)]
     [objs, (object-derivation ctx objs)]))
 
-;; Common Operations with Contexts
+;;; Common Operations with Contexts
 
 (defn dual-context
   "Dualizes context ctx, that is $(G,M,I)$ gets $(M,G,I^{-1})$."

	     att (attributes ctx)
	     uda (up-down-arrows ctx)]
	 (and (forall [g obj]
		(exists [ [h _] uda ]
		  (= g h)))
	      (forall [m att]
		(exists [ [_ n] uda ]
		  (= m n)))))))

(defn context-object-closure

	inz (incidence ctx)
	prime (memoize (partial attribute-derivation ctx))]
    (set-of [g m]
	    [g obj,
	     m att
	     :when (and (not (inz [g m]))
			(forall [n att]
